Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.89   5.341%   $60.9819   $60.98   $61.00   $61.00  
  Purchase #2 $231.60   10.665%   $256.3001   $256.30   $256.30   $256.30  
  Purchase #3 $145.53   8.533%   $157.9481   $157.95   $157.95   $157.90  
  Purchase #4 $14.31   7.149%   $15.333   $15.33   $15.35   $15.30  
  Purchase #5 $9.53   11.352%   $10.6118   $10.61   $10.60   $10.60  
  Purchase #6 $89.61   5.587%   $94.6165   $94.62   $94.60   $94.60  
  Purchase #7 $210.49   9.373%   $230.2192   $230.22   $230.20   $230.20  
  7 purchase totals = $758.96       $826.0106   $826.01   $826.00   $825.90